1. Field of the Invention
This invention relates to a joint apparatus which connects a couple of rods oscillatably in three dimensional directions and more particularly to a technique for controlling the angle of oscillation, which can be effectively used, for example, in a joint apparatus provided between a crank arm and a rod in a wiper apparatus mounted on a vehicle such as an automobile.
2. Related Art Statement
There has been a wiper apparatus for wiping automobile window glass, which comprises a crank arm rotated by a motor; a connecting rod (hereinafter referref to as a rod) for converting the rotation of the crank arm into reciprocating motion so as to reciprocatively rotate a linkage connected with a wiper arm; and a joint apparatus provided between the crank arm and the rod for enabling three dimensional oscillation.
Among joint apparatuses used in such a wiper apparatus, there has been one in which spherical bearing members of resin as joint members are integrally formed (hereinafter referred to as outsert-molding) at both ends of the rod, and spherical shafts as pair joint members are inserted respectively into the spherical bearing members.
In the joint apparatus thus-described, in order to prevent the spherical shaft from falling off the spherical bearing member, a circular concave portion is recessed at the top of the spherical shaft; a circular convex portion which is smaller than the concave portion, is projectingly provided at the spherical bearing member; and the convex portion is inserted in the concave portion. When the rod is bent in the direction perpendicular to its axial direction, the concave and the convex parts in this joint apparatus are designed to interfere mutually in order to prevent an accident in which the spherical shaft falls off the spherical bearing member and to control excess relative swing movement between the spherical shaft and the spherical bearing member.
However, in the above joint apparatus, the concave and the convex parts in the spherical shaft and the spherical bearing member are respectively formed to similar large and small circular shapes so that the angle .theta. of oscillation formed by the spherical shaft and the spherical bearing member, which is delimited by the concave and the convex, parts has the same maximal value for the all circumferential directions, inviting the following problems.
(1) In the wiper apparatus, the maximum value of the inclination angle .alpha. formed by the rod and the crank arm (hereinafter referred to as lengthwise angle) is determined by the relation L/O of the distance L between the spherical centers to the fall O between the spherical centers in a pair of joint apparatuses mounted at both ends of the rod. The lengthwise angle .alpha. is essential for the operation of the wiper system and as a result the oscillation angle .theta. must not be set smaller than the lengthwise angle .alpha.. As a consequence, the angle of rotation .beta. (hereinafter referred to as widthwise angle) having its center on the axis of the rod can not be set smaller than the lengthwise angle .alpha..
(2) When the widthwise angle .beta. is large, it makes the sealing of the joint apparatus difficult.
(3) In addition, in the case of curving rod there is a problem that when the widthwise angle .beta. is large, a large widthwise space must be secured.